Method for treating petroleum distillates



1 for treating sour petroleum distillates.

Patented Sept. 25, 1951 umrso smrgs ATENT OFFICE 2,569,370 4 I METHOD FOR-TREATING PETROLEUM DISTILL'ATES. j John G. Browder, Houston, and Alvin R. Smith,

Baytown, Tex., assignorayby m,esne assignments, to Standard Oil Development Company, v Elizabeth, N. J., a corporation of Delaware N0 Drawing. Application February 19, 1949,

' Serial No. 77,448

The present invention is directed to a -method particularly, the invention is directed to the sweetening of sour petroleum distillates in the presence of an alkali metal hydroxide and a mild oxidizing agent. I

Prior to the present invention, it has been known to treat sour petroleum distillates with aqueous alkaline solutions, such as solutions of alkali metal hydroxide, to remove hydrogen sulfide and other acidic bodies, following which the sour distillates were treated with sodium plumbite solution to convert deleterious sulfur compounds to compounds which are largely innocuous. This and other prior art processes relied on the addition of sulfur to cause the conversion of the sulfur compounds from rnercaptans to disulfides. Other processes convert the undesirable compounds by means of lead sulfide Whichis then separated from the gasoline. Frequently, the separation of lead sulfide from they gasoline was not complete, and, consequently same was carried over into storage, which was field have turned to adding certain compounds, such as phenols and amines, to alkaline solutions,; such as sodium hydroxide, to cause conversion through an oxidation mechanism of the (1618-: terious compounds in the sour naphtha. Frequently' such expedients are unsatisfactory in not completely sweetening the product, and an aftertreatment, by one of the well known procedures, becomes necessary.

From the foregoing discussion of the prior art, it will be seen that the petroleum refining industry has been faced with a problem of converting deleterious sulfur compounds present in petroleum distillates to those which donot detri-.

mentally affect the quality of the product.

It is, therefore, the main object of the presentinvention to provide a treating process in which improved results are obtained in converting obection able sulfur compounds to harmless bodies.

Another object of the present invention is to provide an improved sweetening process in which an active material is added to the petroleum distillate being sweetened to catalyze the conversion of deleterious sulfur compounds.

Another object of the present invention .is'to.

More

2 cl ims. (o1. 96%32) provide arr improved sweeteningprocess inwhichreagents are 'em- "separated from the contacted distillate.

"naphth'enic acids containing up to 12 carbon usually dior polycyclic compounds.

small amounts of catalytic ployed; a v I In the foregoing description of vtl'ieprior art, it

: -will-be seen that the prior art workers added.

compounds such as phenols and amines to the alkaline solutions which were employed. to treat sour petroleum distillates. that, in distinction to the prior art workers, im-

proved results may be obtained by adding, catalytie amounts of a naphthenic acid to'the' sour petroleum distillate. Therefore, in accordance with the present invention the foregoing objects may be achieved. by adding to sour petroleum distillates small amounts of naphthem'c acids and then contacting the sour distillates containing the naphthenic acid with a very small catalytic quantity of a solution of an alkali metal hydroxide while maintaining 'in contact therewith a mild oxidizing agent. 7

'Accordingly', it may be seen that the present invention'may be described briefly as involving treating a 'sour petroleum distillate boiling in the range from about 50 to 750, F. by contact- 1 ,ing the distillate with a solution of an alkali "metal hydroxide while maintaining in the sour distillate a catalytic amount of 'a naphthenic acid and adding to the contacted mixture a mild oxidizing agent sufficient to sweeten said distillate, following. which the alkali metal hydroxide is The naphthenic acids employed in the practice of the present invention are those naphthenic acids usually derived from petroleum and having from 6 to'1'6carbon atoms in the molecule. The

atoms are usually monocyclic compounds and those having more than 12 carbon atoms are 7 The naphthenic'acids from petroleum will usually comprise the naphthenic acids employed in the practice of the present invention. The constitution of such naphthenic acids has been discussed extensively by Ellis, in The Chemistry of Petroleum Derivatives," volume 2, Reinhold Publishing Corporation, New York, 1937, page 1110.

Ordinarily, it will be desirable to employ naphthenic acids in the present invention which have beenfextracted from petroleum fractions boilingin the range from 406 to 700 F., and

fractions in this boiling range. acidsmay be obtained by contacting a petroleum fraction containing .themwith a solution of an lka i n ta y x de be ng- Baum a ity We have-now found of about 40 to form an aqueous layer and an oily layer. The aqueous layer may be partially acidified to release phenolic bodies, the phenolic bodies separated therefrom, and the aqueous layer further "acidified tourelease the" naphthenic 5 acids which then may be used in the practice iof. the present invention.

These compounds may be employed in amounts; based on the naphtha, varying .from.0.00.l,.to 1.0,

per cent by volume, with a preferred range fI'OmZ'T-IO about 0.01 to 0.15 per cent by volume. It is to be emphasized that the specified-amountipf .zthe naphthenic acids should be added to the naphthaand not to the alkaline solution."

The alkaline solution employed in the presentqg droxide will be preferred on account of its avail-' ability."

'I'hetemperature at which the treating opera-'- tion; is conducted will usually be atmospherictemperature'and' may-range from' about 60" up; to about 120 Fialthough temperatures up to 200 F. or higher may-sometimes be used. Apre-- ferred temperature-range will be from about 70 to*about 95 Satisfactory results have-been obtainedrat atmospheric temperatures encounterediin-th'e TexasGulf Coast area.

The present invention will be further illustratedby-the fol-lowing specific example.-

EXAMPLE Ahydrogen sulfide .free :high sulfur petroleum distillate boiling in. the kerosene-boilingrange,.- having ,-.a copper number of 50, was. divided into. two portions. .One portion was contactedwith 1%.by. volume of 40, .B. sodiumhydroxide solution in the presence of,,.300% 1 of the theoretical '45 amountof oxygennecessarylto. sweeten naphtha, while the .other portion .had addedlto. it..0.1'%"by. voliunelof naphthenic acids and was. then contacted withl 1% by volume of 40 B. sodium hydroxide solution in .the. presence of 300% "by volume of the theoretical. amount of oxygen required .tosweeten. .After separationof thealkali. metal hydroxidefromthe two treated portions, copper number tests were determined immediate-.

ly, and ,after 1, 3; 5, and 20 hours settling, The

results of these tests are shown inthe following table:

Table;

Copper Number After Settling For,-

The data in column 1 presents .the results of the treatment with sodium. hydroxide solution, and 'oxygen in the absence of naphthenic acids,'.

while. the data in column 2 illustrate the practice of.the present invention. It will be seen from,- the" foregoing data that the addition;'of'naph-" thenic acid to the kerosene in the presence ,of a catalytic quantity of sodium hydroxide" and oxy..-.

after treatment from 50 to 4'7 which dropped to 28 after 1 hour and then slowly to 17 whereas in the absence of naphthenic acids substantially little sweetening was obtained even after 20 hours standings It will also be apparent from the foregoing data that the kerosene treated in accordance with the present invention will slow- 1y sweeten itself on standing.

In the foregoing example, the improvement obtained in the present invention has been illustrated by the copper number test. This is a well known analytical procedure employed in the petroleum industry: A description of the method of test may be found in U. 0. P. Laboratory Test Methods for Petroleum and 'Its Products, third edition, pageH-Sl, Universal Oil Products CompanygChicago, 1947. This test is a measure of the mercaptan sulfur content of the oil being tested.

In the practice of the present invention, it is to be understood that the sour petroleum distillates employed as feed stocks are free from or deficient in catalytic oxidation promoting com pounds such as naphthenic acids and will not sweeten in contact with a mild oxidizing agentl The great majorityand alkali metal hydroxide. of petroleum distillates to be sweetened in general refinery practice will be found to fall in this category. Our invention is concerned with add-' ing -to and/or maintaining in such stocks the stated amounts of naphthenic acids.

Although not illustrated by the example, one of the particular advantages of the present invention resides in the catalytic ellect of the alkali metal hydroxide solution. The alkali metal hydroxide appears to function as a true catalyst since the small amount used may be recycled to treat large quantities of sour petroleum distillatei A'small amount, of the alkali metal hydroxide solution may be entrained in the treated naphtha, and, therefore, it may be necessary to replace the entrained amount with fresh solution. In short, it is contemplated in the practice of the present inventionthat the alkali metal hydroxide solution will be reused over and over again, since it is not necessary to regenerate the alkali metal hydroxide solution.

The invention has been described-and illustratedby employment of a mild oxidizing agent such as oxygen. It is contemplated that mixtures, of oxygen with other gases, such as air, may be employed: It is also contemplated that other mild oxidizing agents such as peroxides, permanganates, and the like may be used. For example, a hydrogen peroxide solution may be employed as the mild oxidizing agent.

In practicing the present invention, it is tov be understood that the petroleum distillate may,

be subjected to a preliminary treatment for removal of hydrogen sulfide if the distillate contains hydrogen sulfide. Such preliminary treatment may include washing with a dilute alkali metal hydroxide solution or blowing with a freeoxygen containing, gas such as air. If hydrogen sulfide "or other acidic compounds are present and are not removed, the alkali metal hydroxide solution employed as the catalyst may very quickly'become seriously depleted in activity.

In-the practice of the invention, it will be desirable to-use an amount of oxygen in excess of the theoretical required to sweeten the sour petroleum distillate. Ordinarily, an amount of about 300% of the theoretical amount to sweeten maybe employed." However, sweetening in acgen'resulted inreduction of the copper'number cordance'with' the presentinvention may be obtained with considerably lesser quantities of oxygen. In fact, sweetening may be obtained in some cases by contact with the oxygen present in the treating vessel. It willbe desirable to employ an amount of oxidizingagent at least equivalent to the theoretical amount required to sweeten.

The invention has been described and exemplified by employment of 1.0% by volume of the catalytic alkali metal hydroxide solution. It is contemplated that as little as 0.1 and as much as 5% by volume, or more, of the alkali metal hydroxide solution, based on the sour naphtha, may be employed. Very good results, however, are obtained with 1% by volume and this amount will be preferred.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and to secure by Letters Patent is:

1. A method for sweetening a sour petroleum distillate containing mercaptans and having a final boiling point no greater than 750 F. which comprises adding to said distillate a naphthenic acid in a small but effective amount no greater than 1% by volume of said distillate and then contacting the distillate containing added naphthenic acid with a small amount no greater than by. volume of said distillate of a solution of an alkali metal hydroxide While adding a suflicient amount of a mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate.

2. A method in accordance with claim 1 in which the alkali metal hydroxide is sodium hydroxide and the mild oxidizing agent is a free oxygen containing gas.

JOHN G. BROWDER. ALVIN R. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,954,959 Stratford Apr. 17, 1934 2,360,537 Ayers Oct. 17, 1944 2,413,945 Bolt Jan. '7, 1947 

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTILLATE CONTAINING MERCAPTANS AND HAVING A FINAL BOILING POINT NO GREATER THAN 750* F. WHICH COMPRISES ADDING TO SAID DISTILLATE A NAPHTHENIC ACID IN A SMALL BUT EFFECTIVE AMOUNT NO GREATER THAN 1% BY VOLUME OF SAID DISTILLATE AND THEN CONTACTING THE DISTILLATE CONTAINING ADDED NAPHTHENIC ACID WITH A SMALL AMOUNT NO GREATER THAN 5% BY VOLUME OF SAID DISTILLATE OF A SOLUTION OF AN ALKALI METAL HYDROXIDE WHILE ADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TO CONVERT THE MERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENED DISTILLATE. 